Metabolic ATP is converted rapidly to IMP and hypoxanthine during platelet secretion. The process is irreversible and represents a net decrease in the available pool of metabolic adenine nucleotides. The conversion probably procedes via myosin ATPase, adenylate kinase, and AMP deaminase, with the last enzyme playing a major role in removing ADP from the adenylate kinase unidirectionally, utilizing both the energy-rich phosphoryl groups in ATP. In common with the enzyme from other sources, platelet AMP deaminase is subject to regulation by monovalent cations, nucleotides (notably ATP and GTP), phosphate and pyrophosphate. AMP deaminase from other sources has been shown to interact, with high affinity and specificity, with the subfragment-2 (S-2) of myosin, and has been localized in skeletal muscle myofibrils in a region consistent with this binding. The interaction with myosin has kinetic significance in the sense that S-2 binding reverses inhibition of AMP deaminase by nucleoside triphosphates. Platelet AMP deaminase exists as a Na plus-stimulated and an ATP-stimulated activity which may represent covalently modified forms of a single enzyme. We intend to purify platelet AMP deaminase in order to characterize it, study its kinetic properties and possible interaction with platelet myosin, and prepare a specific ferritin-labeled antibody in order to determine the enzyme localization in intact platelets in both resting and stimulated states. We will examine the significance of the two separate AMP deaminase activities detected in platelets. We intend to describe the mechanism of regulation of platelet AMP deaminase and relate this mechanism to the localization of the enzyme and its various ligand effectors in the intact platelet before and after secretion and during the course of secretion. We will use deoxycoformycin, a potent inhibitor of AMP deaminase, to help delineate the role of the enzyme in the secretion process.